1. Field of the Invention
This invention relates to a bolt falling prevention structure for preventing the falling of a bolt during a bolt-tightening operation within an electric connection box (having various electric parts mounted therein) mounted on a vehicle such as an automobile.
2. Background
In current automobiles, various operations are effected automatically, and in this connection various kinds of electronic devices for controlling the travel of the automobile, as well as various kinds of electric parts including fuses and relays, are mounted within an electric connection box. The electric connection box contains wiring members including a fuse holder and connectors, and these wiring members are connected to the various electric parts through bus bars and connection wires.
As shown in FIGS. 6 and 7, a conventional electric connection box 31 includes bus bars (electrically-conductive members) 32, 33 and 34, and a bent portion 32a of the bus bar 32 overlaps the connecting bus bar 33 of an L-shape, and these bus bars 32 and 33 are fastened together by a bolt 35 and a nut 36. The connecting bus bar 33 also overlaps the external-connection bus bar 34, and these bus bars 33 and 34 are fastened together by a bolt 38 and a nut 37.
The bus bars 32 and 33, part of the external-connection bus bar 34 and a fuse holder (not shown) are covered by a cover 41. A bus bar-insulating grommet 42 is mounted on that portion (lead-out portion) of the external-connection bus bar 34 which extends through the cover 41.
For effecting the maintenance of this electric connection box 31, it is necessary to remove part of the bus bars 32, 33 and 34, and the bolts 35 and 38 must be removed and again tightened. Therefore, a bolt insertion hole 43 is formed through a portion of the case 41, and a fastening tool 44, such as a torque wrench, is inserted through the bolt insertion hole 43 so as to remove and tighten the bolt 35.
More specifically, for tightening the bolt 35, the bolt 35 is held by the fastening tool 44 as shown in phantom, and the bolt 35 is threaded into the nut 36. In contrast, for loosening and removing the tightened bolt 35, the fastening tool 44 is inserted through the bolt insertion hole 43, and is fitted on the bolt 35, and then is turned, and the bolt 35, disengaged from the nut 36, is held by the fastening tool 44, and is taken out of the cover 41.
Japanese Utility Model Unexamined Publication No. 6-59620 discloses a nut fixing structure for preventing the falling of a nut. As shown in FIG. 8, in this nut fixing structure, a bolt insertion hole 55 is formed through an attachment portion 58 such as an electric connection box, and a bolt insertion hole 53 is formed through a fixing portion 52 such as a fixing wall. A bolt 60 is inserted from the side of the attachment portion 58, and is threaded into a nut 54 provided at the fixing portion 52.
A nut rotation prevention rib 56 of a hexagonal shape for loosely receiving the nut 54 is formed on the fixing portion 52, and the nut 54 is received within this rib 56 in such a manner that the nut 54 is movable in an axial direction, but can not rotate in a circumferential direction.
Therefore, the nut 54 is received within the rib 56, and in this condition, when the bolt 60 is turned by a fastening tool, the threading operation can be effected without the need for fixing the nut 54 by any additional means. The rib 56 is formed into such a height that it extends beyond the distal end of the tightened bolt 60, and hence the distal end of the bolt 60 will not project outwardly from the rib 56.
A cover 50 for closing an open end of the rib 56 is mounted on the rib 56. The cover 50 is molded integrally with the rib 56 through a connecting portion 51, and the cover 50 closes the open end of the rib 56, with a retaining piece portion 57 retained on a retaining portion 59.
With this construction, a wire harness and other members, provided in the vicinity of the fixing portion, will not contact the distal end of the bolt 60, and therefore will not be damaged. The cover 50 has a nut support portion 62 which supports the nut 54 when the cover 50 is in its closed position. This nut support portion 62 is made of an elastic material, and has, for example, a hexagonal shape, and is fitted in the rib 56, the nut support portion 62 being hollow so that it will not contact the bolt 60. When the cover 50 is closed, the nut support portion 62 supports the nut 54, and urges the nut 54 against a bottom surface 56a of the rib 56 by its elastic force.
Therefore, the height of the nut support portion 62 from the cover 50 is larger than the distance H between the nut 54 and the distal end of the rib 56.
In the above nut fixing structure, if the bolt 60 and the nut 54 are insufficiently fastened together, the bolt 60 is raised in the axial direction as shown in phantom, and therefore the fastened condition can be confirmed with the eyes.
Therefore, the operator further tightens the bolt in an amount corresponding to the amount of rising of the bolt, so that the completely-fastened condition can be achieved.
When the bolt 60 is loosened, and is disengaged from the nut 54, the nut 54 is supported by the nut support portion 62, and therefore will not roll out of the rib 56, so that the bolt can again be tightened relative to the nut 54.
Japanese Utility Model Unexamined Publication No. 5-11723 discloses a bolt fixing clip for fixing a bolt. As shown in FIGS. 9 to 11, the clip 71, molded into an integral construction, includes a wire fixing portion 72, and a bolt retaining portion 73 connected to the wire fixing portion 72 by a connecting portion 81.
A cone-shaped claw portion 76 is provided within a cylindrical barrel portion 77, and is connected to an inner surface of this barrel portion 77. The claw portion 76 is divided by a plurality of grooves 83, and has two small piece portions 78 as shown in FIG. 11. In this claw portion 76, a distal end of its body and distal ends 82b of the small piece portions 78 jointly form one circumferential edge portion, and this portion is retainingly engaged with a bolt 74.
Each small piece portions 78 is in the form of a narrow rectangular plate, and is connected by a hinge portion 80 to the inner surface of the barrel portion 77 intermediate the opposite ends thereof, and is separated from the barrel portion 77 and the claw portion 76, and is gently curved or bent in the vicinity of the hinge portion 80. A flexure prevention rib 79 is formed on a rear surface of the small piece portion 78, and extends from the distal end 82b in the longitudinal direction, the flexure prevention rib 79 being spaced a predetermined distance from the barrel portion 77.
When the bolt retaining portion 73 of the clip 71 is pressed onto the bolt 74 mounted on a body 75, the distal end of the claw portion 76 is retained in a groove of a screw thread of the bolt 74, so that the clip 71 is fixed to the body 75. At this time, the distal end 82b of each of the small piece portions 78 is turned about the hinge portion 80, thereby ensuring the mounting of the clip 71 on the body 75.
In the above retained condition, when a load F is exerted on the retaining portion 73, the whole of the retaining portion 73 is tilted as shown in phantom, and the small piece portion 78 is pushed by the screw thread of the bolt 74, and tends to be turned about the hinge portion 80. However, since the rib 79 is formed on the rear surface of the small piece portion 78, the displacement of the small piece portion 78 is prevented, so that the distal end of the claw portion 76 is kept engaged with the screw thread of the bolt 74. Therefore, the claw portion 76 is prevented from being displaced relative to the bolt 74, and therefore the clip 71 will not be disengaged from the bolt 74, thereby preventing the disengagement of the bolt.
However, in the electric connection box 31 described above with reference to FIGS. 6 and 7, when tightening or removing the bolt 35 by the use of the fastening tool 44, the bolt 35 is merely fitted in the fastening tool 44, and therefore is liable to fall within the case 41. If the bolt 35, which has thus fallen, is left as it is, there is a possibility of an accident such as the short-circuiting of the bus bar 32 or the bus bar 34, and therefore there is encountered a problem that the bolt 35 must be picked up after the case 41 is removed, and then the case 41 must be again fixed.
In addition, if the bolt 35 falls during the removal of the bus bar 32, for example, for maintenance purposes after the electric connection box 31 is mounted on the vehicle, it is necessary to remove the electric connection box 31 from the vehicle, and then to remove the case 41 so as to pick up the bolt 35, and then to mount these parts in their respective original positions. Thus, there is encountered a problem that such a cumbersome operation is needed.
For tightening the bolt 35, the fastening operation can be effected while provisionally retaining the bolt 35 relative to the fastening tool 44 by a tape or the like. However, the provisional retaining of the bolt 35 by the tape or the like requires additional time and labor, and this worsens the efficiency of the operation, and besides when removing the bolt 35, the provisional retaining by the tape can not be used, and there is a high possibility that the bolt 35 falls off the fastening tool 44, and this method is not entirely effective in solving the above problem.
In the nut fixing structure described above with reference to FIG. 8, although the falling of the nut can be prevented, the holding of the bolt is not effected at all, and the problem described above for FIGS. 6 and 7 can not be solved.
In the bolt fixing clip described above with reference to FIGS. 9 to 11, although the disengagement of the bolt can be prevented, the falling of the bolt off the fastening tool can not be prevented when tightening and removing the bolt, and the problem described above for FIGS. 6 and 7 can not be solved.